Generally, a vehicle having an automatic transmission apparatus is provided with a torque converter, which serves as a clutch apparatus and which is provided on a power transmission path between an internal combustion engine and the transmission apparatus. The torque converter is configured so as to continuously transmit a torque generated by the internal combustion engine while the torque converter is shifted from a stalled state to a directly connected state. There exists a torque converter having a lock-up clutch, which is configured so as to directly connect a pump impeller and a turbine runner in order to absorb a rotational difference between the pump impeller and the turbine runner when the rotational difference therebetween is relatively small, which may result in improving fuel consumption. The torque converter having the lock-up clutch is configured to include three hydraulic circuits. More specifically, the torque converter having the lock-up clutch is provided with a supply hydraulic circuit for supplying oil between the pump impeller and the turbine runner, a release hydraulic circuit for discharging the oil existing between the pump impeller and the turbine runner, and a lock-up clutch actuating hydraulic circuit for supplying the oil in order to actuate the lock-up clutch.
Disclosed in JP2003-028271A is an example of a torque converter (a clutch apparatus) having three hydraulic circuits. The torque converter disclosed in JP2003-028271A is configured so that a first hydraulic circuit (which corresponds to the lock-up clutch actuating hydraulic circuit) includes a hollow portion of a pipe member provided within a hollow portion of an input shaft in a concentric manner, a second hydraulic circuit (which corresponds to the release hydraulic circuit) includes a clearance formed between an outer circumferential portion of the pipe member and an inner circumferential portion of the input shaft, and a third hydraulic circuit (which corresponds to the supply hydraulic circuit) includes a clearance formed between an outer circumferential portion of the input shaft and an inner circumferential portion of a stator shaft facing the outer circumferential portion of the input shaft.
There exists a torque converter that has a lock-up clutch, which has the above-mentioned configuration, and furthermore, a mechanism (an impeller clutch), which is configured so as to disengage a pump impeller from an internal combustion engine, in order to reduce a fluid resistance generated between a turbine runner and the pump impeller, which is aimed to reduce fuel consumption while the internal combustion engine is in an idle state. The converter having the lock-up clutch and the impeller clutch generally needs four hydraulic circuits, more specifically, a supply hydraulic circuit, a release hydraulic circuit, a lock-up clutch actuating hydraulic circuit and an impeller clutch operating hydraulic circuit, which is used to supply oil in order to actuate the impeller clutch.
A configuration of the hydraulic circuits of the torque converter disclosed in JP2003-028271A may be modified as follows in order to include four hydraulic circuits. For example, the first hydraulic circuit (which corresponds to the lock-up clutch actuating hydraulic circuit) may include a hollow portion of a second pipe member, which is provided within the hollow portion of the pipe member in a concentric manner, the second hydraulic circuit (which corresponds to the release hydraulic circuit) may include a clearance formed between an inner circumferential portion of the pipe member, which is provided within the hollow portion of the input shaft in the concentric manner, and an outer circumferential portion of the second pipe member, the third hydraulic circuit (which corresponds to the supply hydraulic circuit) may include a clearance formed between the outer circumferential portion of the pipe member and the inner circumferential portion of the input shaft, and a fourth hydraulic circuit (which corresponds to the impeller clutch actuating hydraulic circuit) may include a clearance formed between the outer circumferential portion of the input shaft and the inner circumferential portion of the stator shaft facing to the outer circumferential portion of the input shaft.
However, according to the torque converter disclosed in JP2003-028271A in which the pipe member is arranged within the hollow portion of the input shaft, a diameter of the input shaft may be accordingly enlarged. Furthermore, as mentioned above, in the case where the torque converter disclosed in JP2003-028271A is modified so as to arrange the second pipe member within the hollow portion of the pipe member in order to form four hydraulic circuits within the torque converter, the diameter of the input shaft is further enlarged.
Still further, in the case where the torque converter disclosed in JP2003-028271A is modified so as to provide the second pipe member within the hollow portion of the pipe member in order to form four hydraulic circuits, additional passage bores need to be formed at the input shaft. The passage bores need to be formed at the input shaft so as to be displaced from each other in an axial direction of the input shaft. Therefore, providing the additional passage bores on the input shaft may result in elongating a length of the input shaft in the axial direction. Furthermore, in the case where the additional passage bores are formed on the input shaft, an additional sealing member needs to be provided between the neighboring passage bores, which may result in further elongating the length of the input shaft in the axial direction.
A need thus exists to provide a clutch apparatus which is not susceptible to the drawback mentioned above.